Mechanism of NKT cell-mediated transplant tolerance

Immune cell profiling in intestinal transplantation

Since the first published case study of human intestinal transplantation in 1967, there have been significant studies of intestinal transplant immunology in both animal models and humans. An improved understanding of the profiles of different immune cell subsets is critical for understanding their contributions to graft outcomes. While different studies have focused on the contribution of one or a few subsets to intestinal transplant, no study has integrated these data for a comprehensive overview of immune dynamics after intestinal transplant. Here, we provide a systematic review of the literature on different immune subsets and discuss their roles in intestinal transplant outcomes on multiple levels, focusing on chimerism and graft immune reconstitution, clonal alloreactivity, and cell phenotype. In Sections 1, 2 and 3, we lay out a shared framework for understanding intestinal transplant, focusing on the mechanisms of rejection or tolerance in the context of mucosal immunology and illustrate the unique role of the bidirectional graft-versus-host (GvH) and host-versus-graft (HvG) alloresponse. In Sections 4, 5 and 6, we further expand upon these concepts as we discuss the contribution of different cell subsets to intestinal transplant. An improved understanding of intestinal transplantation immunology will bring us closer to maximizing the potential of this important treatment.

Role of NK T cells in transplantation with particular emphasis on corneal transplantation

Natural killer T cells (NKT cells) are a unique subset of the immune system that possess characteristics of both an innate and adaptive immune response. This study reviews the reported roles of NKT cells in different solid transplantations such as cardiac, skin, liver, and corneal grafts as well as investigates a novel role of NKT cells in steroid-resistant corneal rejections. It is unknown why there is late corneal graft rejection despite being treated with immunosuppression. Our experimental data suggests NKT cells are playing a crucial part in steroid-resistant late graft rejections. While the pathophysiology of acute rejection is better understood, the process of chronic graft rejection is much less clear. Our data suggests NKT cells as a potential therapeutic target to prevent chronic transplant rejection which needs further investigation.

Innate (and Innate-like) Lymphoid Cells: Emerging Immune Subsets With Multiple Roles Along Transplant Life

Transplant immunology is currently largely focused on conventional adaptive immunity, particularly T and B lymphocytes, which have long been considered as the only cells capable of allorecognition. In this vision, except for the initial phase of ischemia/reperfusion, during which the role of innate immune effectors is well established, the latter are largely considered as "passive" players, recruited secondarily to amplify graft destruction processes during rejection. Challenging this prevalent dogma, the recent progresses in basic immunology have unraveled the complexity of the innate immune system and identified different subsets of innate (and innate-like) lymphoid cells. As most of these cells are tissue-resident, they are overrepresented among passenger leukocytes. Beyond their role in ischemia/reperfusion, some of these subsets have been shown to be capable of allorecognition and/or of regulating alloreactive adaptive responses, suggesting that these emerging immune players are actively involved in most of the life phases of the grafts and their recipients. Drawing upon the inventory of the literature, this review synthesizes the current state of knowledge of the role of the different innate (and innate-like) lymphoid cell subsets during ischemia/reperfusion, allorecognition, and graft rejection. How these subsets also contribute to graft tolerance and the protection of chronically immunosuppressed patients against infectious and cancerous complications is also examined.

Donor Treg expansion by liposomal α-galactosylceramide modulates Tfh cells and prevents sclerodermatous chronic graft-versus-host disease

Background and Aim

Chronic graft‐versus‐host disease (cGVHD) is a major cause of nonrelapse morbidity and mortality following hematopoietic stem cell transplantation (HSCT). α‐Galactosylceramide (α‐GC) is a synthetic glycolipid that is recognized by the invariant T‐cell receptor of invariant natural killer T (iNKT) cells in a CD1d‐restricted manner. Stimulation of iNKT cells by α‐GC leads to the production of not only immune‐stimulatory cytokines but also immune‐regulatory cytokines followed by regulatory T‐cell (Treg) expansion in vivo.

Methods

We investigated the effect of iNKT stimulation by liposomal α‐GC just after transplant on the subsequent immune reconstitution and the development of sclerodermatous cGVHD.

Results

Our study showed that multiple administrations of liposomal α‐GC modulated both host‐ and donor‐derived iNKT cell homeostasis and induced an early expansion of donor Tregs. We also demonstrated that the immune modulation of the acute phase was followed by the decreased levels of CXCL13 in plasma and follicular helper T cells in lymph nodes, which inhibited germinal center formation, resulting in the efficient prevention of sclerodermatous cGVHD.

Conclusions

These data demonstrated an important coordination of T‐ and B‐cell immunity in the pathogenesis of cGVHD and may provide a novel clinical strategy for the induction of immune tolerance after allogeneic HSCT.

The Role of Natural Killer Cells in the Immune Response in Kidney Transplantation

Natural killer cells (NK) represent a population of lymphocytes involved in innate immune response. In addition to their role in anti-viral and anti-tumor defense, they also regulate several aspects of the allo-immune response in kidney transplant recipients. Growing evidence suggests a key role of NK cells in the pathogenesis of immune-mediated graft damage in kidney transplantation. Specific NK cell subsets are associated with operational tolerance in kidney transplant patients. On the other side, allo-reactive NK cells are associated with chronic antibody-mediated rejection and graft loss. Moreover, NK cells can prime the adaptive immune system and promote the migration of other immune cells, such as dendritic cells, into the graft leading to an increased allo-immune response and, eventually, to chronic graft rejection. Finally, activated NK cells can infiltrate the transplanted kidney and cause a direct graft damage. Interestingly, immunosuppression can influence NK cell numbers and function, thus causing an increased risk of post-transplant neoplasia or infection. In this review, we will describe how these cells can influence the innate and the adaptive immune response in kidney transplantation and how immunosuppression can modulate NK behavior.

Macrophage Depletion Improves Chronic Rejection in Rats With Allograft Heart Transplantation

BACKGROUND

Macrophages may be important in chronic rejection after organ transplantation. This study aimed to investigate the possibility of depleting macrophages for a certain amount of time to alleviate chronic rejection in a heart transplant model of Fischer to Lewis rats.

METHODS

Clodronate liposome was injected abdominally to deplete macrophages for 2 time frames. The expression levels of ectodysplasin 1, arginase 1 (Arg1), chitinase-like lectin (Ym1), interferon gamma, tumor necrosis factor α (TNF-α), smooth muscle α-actin (α-SMA), monocyte chemoattractant protein 1 (MCP-1), and interleukin 10 (IL-10) were detected.

RESULTS

1. The expression levels of α-SMA, interferon gamma, TNF-α, and MCP-1 and the transformation of peripheral T cells were lower after macrophage depletion for 2 or 4 weeks. 2. The expression levels of α-SMA, TNF-α, and MCP-1 and the transformation of peripheral T cells were even lower after 4 weeks compared with 2 weeks, except for interferon gamma. 3. A higher level of expression of Arg1 and Ym1 after macrophage depletion for 2 weeks was observed. 4. A higher level of expression of IL-10 after macrophage depletion for 2 weeks, but not 4 weeks, was also observed.

CONCLUSIONS

Macrophage clearance after heart transplantation alleviated chronic rejection probably via M2 polarization of regenerated macrophages, reduced T-lymphocyte proliferation, and changed the expression levels of interferon gamma, TNF-α, MCP-1, and IL-10.

Evolutionary Underpinnings of Innate-Like T Cell Interactions with Cancer

Cancers impose a significant health and economic burden. By harnessing the immune system, current immunotherapies have revolutionized the treatment against human cancers and potentially offer a long-term cure. Among others, innate-like T (iT) cells, including natural killer T cells, are promising candidates for immunotherapies. Unlike conventional T cells, iT cells regulate multiple immune processes and express an invariant T cell receptor that is shared among different individuals. However, the conditions that activate the pro- and antitumor functions of iT cells are partially understood. These gaps in knowledge hamper the use of iT cell in clinics. It might be beneficial to examine the roles of iT cells in an alternative animal model - the amphibian Xenopus whose immune system shares many similarities to that of mammals. Here, we review the iT cell biology in the context of mammalian cancers and discuss the challenges currently found in the field. Next, we introduce the advantages of Xenopus as a model to investigate the role of iT cells and interacting major histocompatibility complex (MHC) class I-like molecules in tumor immunity. In Xenopus, 2 specific iT cell subsets, Vα6 and Vα22 iT cells, recognize and fight tumor cells. Furthermore, our recent data reveal the complex functions of the Xenopus MHC class I-like (XNC) gene XNC10 in tumor immune responses. By utilizing reverse genetics, transgenesis, and MHC tetramers, we have a unique opportunity to uncover the relevance of XNC genes and iT cell in Xenopus tumor immunity.

Circulating NK cell subsets and NKT‑like cells in renal transplant recipients with acute T‑cell‑mediated renal allograft rejection

Emerging evidence indicates that natural killer (NK) cells and NKT-like cells may affect allograft outcomes following solid organ transplantation. However, the roles of these cells in allograft acceptance and dysfunction are controversial. To assess the changes in NK cell and CD3⁺CD56⁺ NKT-like cell frequency and phenotype in renal allograft recipients and to explore their associations with acute T-cell-mediated renal allograft rejection (ACR), longitudinal changes in NK and NKT-like cell frequency and phenotype were characterized using flow cytometry and immunohistochemistry in the peripheral blood and kidney allograft tissues in 142 recipients undergoing kidney transplantation. The serum concentrations of NK cell-associated cytokines were also detected by cytokine multiplex immunoassay. In contrast to the healthy controls, recipients with stable graft function exhibited increased proportions of CD56^brightCD16^dim subsets and decreased proportions of NKT-like cells in their peripheral blood mononuclear cells (PBMCs). Patients with ACR demonstrated increased proportions of NK cells, which were associated with increased CD3⁻CD56^bright subsets and decreased CD3⁻CD56^dim subsets, an increase in the CD56^bright/CD56^dim ratio in PBMCs and increased CD56⁺ NK cell infiltration in the kidney allograft, compared with the stable controls. In addition, there was a decreased proportion of NKT-like cells in patients with ACR, and an increased ratio of CD56^bright/NKT-like cells compared with the stable controls. These differences appeared to be consistent with the increase in the serum concentrations of C-C motif chemokine 19 and the decrease in the serum concentrations of interleukin-15. These data indicate that CD56^bright NK cells may promote the development of ACR, and that NKT-like cells may have immunoregulatory function. The results also imply that the CD56^bright/CD56^dim ratio may affect the ACR signatures.

Old game, new players: Linking classical theories to new trends in transplant immunology

The evolutionary emergence of an efficient immune system has a fundamental role in our survival against pathogenic attacks. Nevertheless, this same protective mechanism may also establish a negative consequence in the setting of disorders such as autoimmunity and transplant rejection. In light of the latter, although research has long uncovered main concepts of allogeneic recognition, immune rejection is still the main obstacle to long-term graft survival. Therefore, in order to define effective therapies that prolong graft viability, it is essential that we understand the underlying mediators and mechanisms that participate in transplant rejection. This multifaceted process is characterized by diverse cellular and humoral participants with innate and adaptive functions that can determine the type of rejection or promote graft acceptance. Although a number of mediators of graft recognition have been described in traditional immunology, recent studies indicate that defining rigid roles for certain immune cells and factors may be more complicated than originally conceived. Current research has also targeted specific cells and drugs that regulate immune activation and induce tolerance. This review will give a broad view of the most recent understanding of the allogeneic inflammatory/tolerogenic response and current insights into cellular and drug therapies that modulate immune activation that may prove to be useful in the induction of tolerance in the clinical setting.

Donor bone marrow cells are essential for iNKT cell-mediated Foxp3+ Treg cell expansion in a murine model of transplantation tolerance

Mixed chimerism induction is the most reliable method for establishing transplantation tolerance. We previously described a novel treatment using a suboptimal dose of anti-CD40 ligand (anti-CD40L) and liposomal formulation of a ligand for invariant natural killer T cells administered to sub-lethally irradiated recipient mice after donor bone marrow cell (BMC) transfer. Recipient mice treated with this regimen showed expansion of a Foxp3-positive regulatory T(Treg) cell phenotype, and formation of mixed chimera. However, the mechanism of expansion and bioactivity of Treg cells remains unclear. Here, we examine the role of donor BMCs in the expansion of bioactive Treg cells. The mouse model was transplanted with a heart allograft the day after treatment. The results showed that transfer of spleen cells in place of BMCs failed to deplete host interferon (IFN)-γ-producing CD8⁺ T cells, expand host Ki67⁺ CD4⁺ CD25⁺ Foxp3⁺ Treg cells, and prolong graft survival. Severe combined immunodeficiency mice who received Treg cells obtained from BMC-recipients accepted skin grafts in an allo-specific manner. Myeloid-derived suppressor cells, which were a copious cell subset in BMCs, enhanced the Ki67 expression of Treg cells. This suggests that donor BMCs are indispensable for the expansion of host bioactive Treg cells in our novel treatment for transplant tolerance induction.

Cellular immune profile of kidney transplant patients developing anti-HLA antibodies during childhood

BACKGROUND

In the field of kidney transplantation, identifying early signatures of humoral rejection is a key challenge.

METHODS

We investigated the presence of anti-HLA antibodies and the distribution of lymphocyte subpopulations in 77 kidney-transplanted children and young adults compared to 23 healthy controls. Moreover, we tested whether the presence of anti-HLA antibodies could be related to modification in lymphocyte phenotype. Finally, we correlated the presence of anti-HLA antibodies and specific alteration of lymphocyte subsets with clinical outcomes.

RESULTS

In kidney-transplanted children who developed anti-HLA antibodies, we observed an expansion of double-negative B cells (CD19 + CD27-IgD-), indicating premature aging of this compartment. Moreover, we reported signs of impaired B cell regulation, indicated by a higher IL-21R+ B cell frequency associated with an abnormal increase of follicular helper T cells. Finally, a considerable reduction in CD8+ effector T and invariant Natural killer T (NKT) cells was observed. The stability of graft function over time is significantly correlated with the frequency of peripheral effector CD4+ and CD8+ T cells and invariant NKT cells.

CONCLUSIONS

This study supports the usefulness of lymphocyte subset as one of a spectrum of early diagnostic tools required to identify patients at risk of developing donor alloimmune response.

Clonal Deletion Established via Invariant NKT Cell Activation and Costimulatory Blockade Requires In Vivo Expansion of Regulatory T Cells

Recently, the immune-regulating potential of invariant natural killer T (iNKT) cells has attracted considerable attention. We previously reported that a combination treatment with a liposomal ligand for iNKT cells and an anti-CD154 antibody in a sublethally irradiated murine bone marrow transplant (BMT) model resulted in the establishment of mixed hematopoietic chimerism through in vivo expansion of regulatory T cells (Tregs). Herein, we show the lack of alloreactivity of CD8(+) T cells in chimeras and an early expansion of donor-derived dendritic cells (DCs) in the recipient thymi accompanied by a sequential reduction in the donor-reactive Vβ-T cell receptor repertoire, suggesting a contribution of clonal deletion in this model. Since thymic expansion of donor DCs and the reduction in the donor-reactive T cell repertoire were precluded with Treg depletion, we presumed that Tregs should preform before the establishment of clonal deletion. In contrast, the mice thymectomized before BMT failed to increase the number of Tregs and to establish CD8(+) T cell tolerance, suggesting the presence of mutual dependence between the thymic donor-DCs and Tregs. These results provide new insights into the regulatory mechanisms that actively promote clonal deletion.

Tolerogenic Dendritic Cells on Transplantation: Immunotherapy Based on Second Signal Blockage

Dendritic cells (DCs), the most important professional antigen-presenting cells (APC), play crucial role in both immunity and tolerance. It is well known that DCs are able to mount immune responses against foreign antigens and simultaneously tolerate self-antigens. Since DCs can be modulated depending on the surrounding microenvironment, they can act as a bridge between innate and adaptive immunity. However, the mechanisms that support this dual role are not entirely clear. Recent studies have shown that DCs can be manipulated ex vivo in order to trigger their tolerogenic profile, what can be a tool to be used in clinical trials aiming the treatment of various diseases and the prevention of transplant rejection. In this sense, the blockage of costimulatory molecules on DC, in the attempt of inhibiting the second signal in the immunological synapse, can be considered as one of the main strategies under development. This review brings an update on current therapies using tolerogenic dendritic cells modulated with costimulatory blockers with the aim of reducing transplant rejection. However, although there are current clinical trials using tolerogenic DC to treat allograft rejection, the actual challenge is to modulate these cells in order to maintain a permanent tolerogenic profile.

Accumulation of invariant NKT cells with increased IFN-γ production in persistent high-risk HPV-infected high-grade cervical intraepithelial neoplasia

BACKGROUND

Persistent high-risk human papillomavirus (HR-HPV) infection has been implicated in the development of high-grade cervical intraepithelial neoplasia (CIN) and cervical cancer. Invariant natural killer T (iNKT) cells produce large amounts of cytokines to regulate immune responses. However, the role of iNKT cells in human persistent HPV-infected cervical tissues is unknown.

METHODS

In our study, 201 patients with diagnoses ranging from normal ectocervical tissue to CINIII from June 2010 to May 2012 were enrolled. HPV DNA and HPV types were detected using the hybrid capture-2 HPV DNA test. Flow cytometry was used to investigate iNKT and CD3+ T cell infiltration into cervical tissues. Real-time quantitative reverse transcription-polymerase chain reaction was used to study IFN-γ expression and immunohistochemistry was used to determine CD3+ T cell distribution.

RESULTS

A significant increase in iNKT cells was observed in HPV-positive cervical tissues (p < 0.05), especially in CINII-III (p < 0.01). IFN-γ expression was also increased in HPV-positive cervical tissues (p < 0.05). CD3+ T cells were detected among both epithelium and stromal layers in cervical tissues, and the percentage of CD3+ T cells in HPV-positive cervical tissues was similar to that in HPV-negative cervical tissues (p > 0.05).

CONCLUSIONS

The iNKT cell aggregation in cervical tissues during the progression from HPV infection to CIN indicates that iNKT cells might play an important role in suppressing immunity. IFN-γ expression could also be related to the HPV infection status. Preventing the accumulation or functioning of iNKT cells in cervical tissues may be a viable method to prevent the development of CIN.

VIRTUAL SLIDES

The virtual slides for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/2521874671514142.

Cellular mechanisms of CCL22-mediated attenuation of autoimmune diabetes

Autoimmune destruction of insulin-producing β cells in type 1 diabetes and islet transplantation involves a variety of immune pathways but is primarily mediated by self-reactive T cells. Chemokines can modulate local immune responses in inflammation and tumors by recruiting immune cells. We have reported that expression of the chemokine CCL22 in pancreatic β cells in the NOD mouse prevents autoimmune attack by recruiting T regulatory cells (Tregs), protecting mice from diabetes. In this study we show that invariant NKT cells are also recruited to CCL22-expressing islet transplants and are required for CCL22-mediated protection from autoimmunity. Moreover, CCL22 induces an influx of plasmacytoid dendritic cells, which correlates with higher levels of IDO in CCL22-expressing islet grafts. In addition to its chemotactic properties, we found that CCL22 activates Tregs and promotes their ability to induce expression of IDO by dendritic cells. Islet CCL22 expression thus produces a tolerogenic milieu through the interplay of Tregs, invariant NKT cells, and plasmacytoid dendritic cells, which results in suppression of effector T cell responses and protection of β cells. The immunomodulatory properties of CCL22 could be harnessed for prevention of graft rejection and type 1 diabetes as well as other autoimmune disorders.

A novel approach inducing transplant tolerance by activated invariant natural killer T cells with costimulatory blockade

Invariant natural killer T (iNKT) cells are one of the innate lymphocytes that regulate immunity, although it is still elusive how iNKT cells should be manipulated for transplant tolerance. Here, we describe the potential of a novel approach using a ligand for iNKT cells and suboptimal dosage of antibody for CD40-CD40 ligand (L) blockade as a powerful method for mixed chimerism establishment after allogenic bone marrow transplantation in sublethally irradiated fully allo recipients. Mixed-chimera mice accepted subsequent cardiac allografts in a donor-specific manner. High amounts of type 2 helper T cytokines were detected right after iNKT cell activation, while subsequent interferon-gamma production by NK cells was effectively inhibited by CD40/CD40L blockade. Tolerogenic components, such as CD11c(low) mPDCA1(+) plasmacytoid dendritic cells and activated regulatory T cells (Tregs) expressing CD103, KLRG-1 and PD-1, were subsequently augmented. Those activating Tregs seem to be required for the establishment of chimerism because depletion of the Tregs 1 day before allogenic cell transfer resulted in a chimerism brake. These results collectively suggest that our new protocol makes it possible to induce donor-specific tolerance by enhancement of the innate ability for immune tolerance in place of the conventional immunosuppression.

Progress in research of IL-10 and IL-17 in chronic hepatitis B, hepatitis B virus-related liver cirrhosis and cirrhosis with abdominal infection

Hepatitis B is a global contagious disease, posing a serious threat to human health. However, its pathogenic mechanisms and how it ultimately leads to the formation of cirrhosis are not fully understood. Elucidating the progression of hepatitis B and the mechanism responsible for liver cirrhosis formation can help develop novel antiviral treatment and anti-fibrosis therapy. In recent years, great progress has been made in understanding the pathogenesis of chronic hepatitis and liver cirrhosis and their treatment. Cytokines have become a research hotspot in this field. Emerging evidence suggests that a variety of cytokines in the liver have a quite significant role in the progressive process of HBV. Cytokines mainly mediate cell-cell interactions in paracrine, feedback or other manners to participate in the pathogenesis of chronic hepatitis B, cirrhosis and cirrhosis with infection. In recent years, many studies suggest that serum interleukin-10 (IL-10) and IL-17 levels are correlated with the development and prognosis of chronic hepatitis B, liver cirrhosis and cirrhosis with infection. In this paper, we review the progress in research of IL-10 and IL-17 in chronic hepatitis B, liver cirrhosis and cirrhosis with infection.

Targeted delivery of curcumin for treating type 2 diabetes

Type 2 diabetes is a chronic condition in which cells have reduced insulin signalling, leading to hyperglycemia and long-term complications, including heart, kidney and liver disease. Macrophages activated by dying or stressed cells, induce the transcription factor nuclear factor kappa-B leading to the production of pro-inflammatory cytokines including TNF and IL-6. These inflammatory macrophages in liver and adipose tissue promote insulin resistance, and medications which reduce inflammation and enhance insulin signalling improve glucose control. Curcumin is an anti-oxidant and nuclear factor kappa-B inhibitor derived from turmeric. A number of studies have shown that dietary curcumin reduces inflammation and delays or prevents obesity-induced insulin resistance and associated complications, including atherosclerosis and immune mediate liver disease. Unfortunately dietary curcumin is poorly absorbed by the digestive system and undergoes glucuronidation and excretion rather than being released into the serum and systemically distributed. This confounds understanding of how dietary curcumin exerts its beneficial effects in type 2 diabetes and associated diseases. New improved methods of delivering curcumin are being developed including nanoparticles and lipid/liposome formulations that increase absorption and bioavailability of curcumin. Development and refinement of these technologies will enable cell-directed targeting of curcumin and improved therapeutic outcome.

NK cells are required for costimulatory blockade induced tolerance to vascularized allografts

BACKGROUND

The role of natural killer (NK) cells in organ transplantation is poorly understood because studies link these cells to both regulatory and inflammatory functions. NK cells exacerbate inflammation and adaptive immunity under conditions of allograft rejection, but little is known regarding their roles in allograft tolerance. We test the hypothesis that NK cells have regulatory function and promote tolerance induction to murine cardiac allografts.

METHODS

Murine hearts were transplanted as fully vascularized heterotopic grafts from BALB/c donors into C57BL/6 recipients. Allograft tolerance was achieved using donor splenocyte transfusion + anti-CD40L monoclonal antibody (mAb) before transplantation. The requirement for NK cells in tolerance induction was tested by administering anti-NK1.1-depleting mAb or anti-NKG2D-blocking mAb. Intragraft and peripheral immune cell populations were determined by flow cytometry and immunohistochemistry. CD4 T-cell alloantigen-specific responses and donor-specific alloantibody were also determined.

RESULTS

NK cell-depleted recipients acutely reject allografts despite anti-CD40L blockade, but rejecting recipients lacked alloantibody and alloantigen-specific CD4 T-cell responses. NK cell depletion resulted in elevated numbers of graft-infiltrating macrophages. NKG2D blockade in tolerized recipients did not cause acute rejection but increased macrophage graft infiltration and increased the expression of NKG2D ligand Rae-1γ on these cells.

CONCLUSIONS

Our data show that NK cells are required for tolerance induction in recipients given donor splenocyte transfusion + anti-CD40L mAb. Our data suggest NK cells regulate monocyte or macrophage activation and infiltration into allografts by a mechanism partially dependent on NKG2D receptor-ligand interactions between NK cells and monocytes/macrophages.

Renal allograft recipients fail to increase interferon-γ during invasive fungal diseases

Invasive fungal diseases are a major cause of death in renal allograft recipients. We previously reported that adjunctive recombinant human interferon-γ therapy has clinical utility for invasive fungal diseases after renal transplantation. We have now developed a rapid peripheral blood-based quantitative real-time PCR assay that enables accurate profiling of cytokine imbalances. Our preliminary studies in renal transplant patients with invasive fungal diseases suggest that they fail to mount an adequate interferon-γ response to the fungal infection. In addition, they have reduced IL-10 and increased TNF-α when compared to stable renal transplant patients. These preliminary cytokine profiling-based observations provide a possible explanation for the therapeutic benefit of adjunctive human interferon-γ therapy in renal allograft recipients with invasive fungal diseases.

Increased natural killer T-like cells are a major source of pro-inflammatory cytokines and granzymes in lung transplant recipients

BACKGROUND AND OBJECTIVE

Natural killer T (NKT)-like cells are a small but significant population of T lymphocytes; however, their role in lung transplant and the effect of current immunosuppressive agents on their function is largely unknown. We have previously shown lung transplant rejection was associated with an increase in peripheral blood T cell γ-interferon (IFN-γ), tumour necrosis factor-α (TNF-α) and granzyme B. NKT-like cells are a source of these pro-inflammatory mediators and as such may be involved in lung transplant pathology.

METHODS

We analysed NKT-like cell numbers and cytokine and granzyme profiles in peripheral blood from a group of stable lung transplant patients and control subjects using multiparameter flow cytometry.

RESULTS

There was a significant increase in NKT-like cells in transplant patients compared with control subjects (6.8 ± 4.9 vs 0.8 ± 0.2% lymphocytes respectively). There was an increase in the numbers of NKT-like cells producing IFN-γ, TNF-α, IL-2 IL-17, granzyme and perforin in transplant patients compared with controls. Immunosuppressant drugs were less effective at inhibiting IFN-γ and TNF-α production by T and NKT-like cells than NK cells in vitro.

CONCLUSIONS

Current therapeutics is inadequate at suppressing NKT-like cell numbers and their production of pro-inflammatory mediators known to be associated with graft rejection. Alternative therapies that specifically target NKT-like cells may improve patient morbidity.

Bystander activation of iNKT cells occurs during conventional T-cell alloresponses

It is well established that iNKT cells can be activated by both exogenous and a limited number of endogenous glycolipids. However, although iNKT cells have been implicated in the immune response to transplanted organs, the mechanisms by which iNKT cells are activated in this context remain unknown. Here we demonstrate that iNKT cells are not activated by allogeneic cells per se, but expand, both in vitro and in vivo, in the presence of a concomitant conventional T-cell response to alloantigen. This form of iNKT activation was found to occur independently of TCR-glycolipid/CD1d interactions but rather was a result of sequestration of IL-2 produced by conventional alloreactive T cells. These results show for the first time that IL-2, produced by activated conventional T cells, can activate iNKT cells independently of glycolipid/CD1d recognition. Therefore, we propose that the well-documented involvement of iNKT cells in autoimmunity, the control of cancer as well as following transplantation need not involve recognition of endogenous or exogenous glycolipids but alternatively may be a consequence of specific adaptive immune responses.

Immunology in the Clinic Review Series; focus on host responses: invariant natural killer T cell activation following transplantation

Invariant natural killer T (iNKT) cells have been shown to play a key role in the regulation of immunity in health and disease. However, iNKT cell responses have also been found to influence both rejection and the induction of tolerance following transplantation of allogeneic cells or organs. Although a number of mechanisms have been identified that lead to iNKT cell activation, how iNKT cells are activated following transplantation remains unknown. This review will attempt to identify potential mechanisms of iNKT cell activation in the context of transplantation by applying knowledge garnered from other disease situations. Furthermore, we put forward a novel mechanism of iNKT cell activation which we believe may be the dominant mechanism responsible for iNKT activation in this setting, i.e. bystander activation by interleukin-2 secreted by recently activated conventional T cells.

Distinct and overlapping effector functions of expanded human CD4+, CD8α+ and CD4-CD8α- invariant natural killer T cells

CD1d-restricted invariant natural killer T (iNKT) cells have diverse immune stimulatory/regulatory activities through their ability to release cytokines and to kill or transactivate other cells. Activation of iNKT cells can protect against multiple diseases in mice but clinical trials in humans have had limited impact. Clinical studies to date have targeted polyclonal mixtures of iNKT cells and we proposed that their subset compositions will influence therapeutic outcomes. We sorted and expanded iNKT cells from healthy donors and compared the phenotypes, cytotoxic activities and cytokine profiles of the CD4(+), CD8α(+) and CD4(-)CD8α(-) double-negative (DN) subsets. CD4(+) iNKT cells expanded more readily than CD8α(+) and DN iNKT cells upon mitogen stimulation. CD8α(+) and DN iNKT cells most frequently expressed CD56, CD161 and NKG2D and most potently killed CD1d(+) cell lines and primary leukemia cells. All iNKT subsets released Th1 (IFN-γ and TNF-α) and Th2 (IL-4, IL-5 and IL-13) cytokines. Relative amounts followed a CD8α>DN>CD4 pattern for Th1 and CD4>DN>CD8α for Th2. All iNKT subsets could simultaneously produce IFN-γ and IL-4, but single-positivity for IFN-γ or IL-4 was strikingly rare in CD4(+) and CD8α(+) fractions, respectively. Only CD4(+) iNKT cells produced IL-9 and IL-10; DN cells released IL-17; and none produced IL-22. All iNKT subsets upregulated CD40L upon glycolipid stimulation and induced IL-10 and IL-12 secretion by dendritic cells. Thus, subset composition of iNKT cells is a major determinant of function. Use of enriched CD8α(+), DN or CD4(+) iNKT cells may optimally harness the immunoregulatory properties of iNKT cells for treatment of disease.

Regulation of immune responses to HPV infection and during HPV-directed immunotherapy

The recent development of vaccines prophylactic against human papillomavirus (HPV) infection has the potential to reduce the incidence of cervical cancer globally by up to 70% over the next 40 years, if universal immunization is adopted. As these prophylactic vaccines do not alter the natural history of established HPV infection, immunotherapies to treat persistent HPV infection and associated precancers would be of benefit to assist with cervical cancer control. Efforts to develop immuno-therapeutic vaccines have been hampered by the relative non-immunogenicity of HPV infection, by immunoregulatory processes in skin, and by subversion of immune response induction and immune effector functions by papillomavirus proteins. This review describes HPV-specific immune responses induced by viral proteins, their regulation by host and viral factors, and highlights some conclusions from our own recent research.

Activation of human invariant natural killer T cells with a thioglycoside analogue of α-galactosylceramide

Activation of CD1d-restricted invariant NKT (iNKT) cells with the glycolipid α-galactosylceramide (α-GalCer) confers protection against disease in murine models, however, clinical trials in humans have had limited impact. We synthesized a novel thioglycoside analogue of α-GalCer, denoted α-S-GalCer, and tested its efficacy for stimulating human iNKT cells in vitro. α-S-GalCer stimulated cytokine release by iNKT cells in a CD1d-dependent manner and primed CD1d(+) target cells for lysis. α-S-GalCer-stimulated iNKT cells induced maturation of monocyte-derived dendritic cells into antigen-presenting cells that released IL-12 and small amounts of IL-10. The nature and potency of α-S-GalCer and α-GalCer in human iNKT cell activation were similar. However, in contrast to α-GalCer, α-S-GalCer did not activate murine iNKT cells in vivo. Because of its enhanced stability in biological systems, α-S-GalCer may be superior to α-GalCer as a parent compound for developing adjuvant therapies for humans.

Reduced levels of both circulating CD4+ CD25+ CD127(low/neg) and CD4+ CD8(neg) invariant natural killer regulatory T cells in stable heart transplant recipients

A cross-regulation between two regulatory T cell (T(reg) ) subsets [CD4(+) CD25(+) and invariant natural killer (NK) T - iNK T] has been described to be important for allograft tolerance induction. However, few studies have evaluated these cellular subsets in stable recipients as correlates of favourable clinical outcome after heart transplantation. T(reg) and iNK T cell levels were assayed by flow cytometry in peripheral blood samples from 44 heart transplant recipients at a 2-year interval in 38 patients, and related to clinical outcome. Multi-parameter flow cytometry used CD4/CD25/CD127 labelling to best identify T(reg) , and a standard CD3/CD4/CD8/Vα24/Vβ11 labelling strategy to appreciate the proportions of iNK T cells. Both subtypes of potentially tolerogenic cells were found to be decreased in stable heart transplant recipients, with similar or further decreased levels after 2 years. Interestingly, the patient who presented with several rejection-suggesting incidents over this period displayed a greater than twofold increase of both cell subsets. These results suggest that CD4(+) CD25(+) CD127(low/neg) T(reg) and iNK T cells could be involved in the local control of organ rejection, by modulating immune responses in situ, in clinically stable patients. The measurement of these cell subsets in peripheral blood could be useful for non-invasive monitoring of heart transplant recipients, especially in the growing context of tolerance-induction trials.

Transplant long-surviving induced by CD40-CD40 ligand costimulation blockade is dependent on IFN-γ through its effect on CD4(+)CD25(+) regulatory T cells

BACKGROUND

IFN-γ was documented to be commonly associated with acute rejection. In the present study, we investigated the role of IFN-γ in the transplant long-surviving induced by blocking CD40-CD40 ligand (CD40-CD40L) costimulation and its mechanisms.

METHODS

IFN-γ expression in cardiac allografts and spleens from syngeneic and allogeneic recipients with or without anti-CD40L monoclonal antibody (MR-1) treatment was examined by real-time RT-PCR. The grafts survival time in Wild type (IFN-γ(+/+)) and IFN-γ deficient (IFN-γ(-/-)) recipients was investigated. Mixed lymphocyte reaction (MLR) of CD4(+) T cells and cytotoxic T lymphocyte (CTL) assay of CD8(+) T cells were also studied. FoxP3 expression in allografts and spleens from IFN-γ(+/+) or IFN-γ(-/-) recipients with MR-1 treatment was examined. Furthermore, FoxP3, IL-10 and CTLA-4 expressions and the suppressive capability of CD4(+)CD25(+) regulatory T cells were examined.

RESULTS

Rejected allografts showed significantly higher IFN-γ expression than long-surviving allografts. Allograft survival was not prolonged in nonimmunosuppressed IFN-γ(-/-) mice. Administration of MR-1 induced long-term survival in 90.1% of IFN-γ(+/+) recipients (98±6.6 days) but failed to do so in IFN-γ(-/-) group (16.2±4.0 days). IFN-γ(-/-) recipients facilitated the proliferation and CTL generation of T cells. The allografts and spleens from IFN-γ(+/+) recipients contained higher FoxP3 expression than IFN-γ(-/-) recipients. Moreover, CD4(+)CD25(+) T cells from IFN-γ(+/+) recipients displayed a higher FoxP3 and IL-10 expression and suppressive capability.

CONCLUSION

IFN-γ plays an important role in the long-surviving induced by blocking CD40-CD40L through inhibiting the function of activated T cells and increasing suppressive capability of CD4(+)CD25(+) regulatory T cells.

Invariant NKT cells in hyperplastic skin induce a local immune suppressive environment by IFN-gamma production

NKT cells can promote or inhibit adaptive immune responses. Cutaneous immunity is tightly regulated by cooperation between innate and adaptive immune processes, but the role of NKT cells in regulating cutaneous immunity is largely unknown. In this study, we show, in a mouse model, that skin-infiltrating CD1d-restricted NKT cells in HPV16-E7 transgenic hyperplastic skin produce IFN-gamma, which can prevent rejection of HPV16-E7-expressing skin grafts. Suppression of graft rejection is associated with the accumulation of CD1d(hi)-expressing CD11c(+)F4/80(hi) myeloid cells in hyperplastic skin. Blockade of CD1d, removal of NKT cells, or local inhibition of IFN-gamma signaling is sufficient to restore immune-mediated graft rejection. Thus, inhibition of NKT cell recruitment or function may enable effective immunity against tumor and viral Ags expressed in epithelial cells.

Lipid and glycolipid antigens of CD1d-restricted natural killer T cells

In spite of their relatively limited antigen receptor repertoire, CD1d-restricted NKT cells recognize a surprisingly diverse range of lipid and glycolipid antigens. Recent studies of natural and synthetic CD1d-presented antigens provide an increasingly detailed picture of how the specific structural features of these lipids and glycolipids influence their ability to be presented to NKT cells and stimulate their diverse immunologic functions. Particularly for synthetic analogues of alpha-galactosylceramides which have been the focus of intense recent investigation, it is becoming clear that the design of glycolipid antigens with the ability to precisely control the specific immunologic activities of NKT cells is likely to be feasible. The emerging details of the mechanisms underlying the structure-activity relationship of NKT cell antigens will assist greatly in the design and production of immunomodulatory agents for the precise manipulation of NKT cells and the many other components of the immune system that they influence.

The specialized iNKT cell system recognizes glycolipid antigens and bridges the innate and acquired immune systems with potential applications for cancer therapy

Invariant NKT (iNKT) cells bridge innate and acquired immunity and play an important role in both protective and regulatory responses. The nature of the response is dictated by the initial cytokine environment: interaction with IL-10-producing cells induces negative regulatory T(h)2/regulatory T cell-type iNKT cells, while that with IL-12-producing cells results in pro-inflammatory T(h)1-type responses. Particularly, in the anti-tumor response, iNKT cells mediate adjuvant activity by their production of IFN-gamma, which in turn activates both innate and acquired immune systems. Thus, upon activation of iNKT cells, both MHC(-) and MHC(+) tumor cells can be efficiently eliminated. On the basis of these mechanisms, iNKT cell-targeted adjuvant cell therapies have been developed and have shown great promise in initial clinical trials on cancer patients.

Two-year follow-up of a prospective study of circulating regulatory T cells in renal transplant patients

CD4(+)CD25(high)FOXP3(+) regulatory T cells (Tregs) are involved in alloreactivity and may be associated with protection from rejection. Their quantification in peripheral blood could guide clinicians in the management of renal transplant patients. Thus, we prospectively monitored the levels and in vitro suppression of circulating Tregs in 33 renal transplant patients from deceased donors within the first two yr of transplantation. Patients received maintenance immunosuppression with tacrolimus, mofetil mycophenolate and prednisolone. Results showed that peripheral blood Tregs were significantly lower six months after transplantation and recovered to almost basal levels at first post-transplant year. The number of circulating Tregs increased significantly over basal levels afterwards. The decrease in circulating Tregs at six months may be explained by the high load of tacrolimus, as demonstrated by the inverse correlation between the blood concentration of Tregs and tacrolimus. Likewise, nine patients treated with anti-CD25 antibodies showed higher numbers of Tregs at six months than those that did not, although differences were not observed later. In conclusion, circulating Tregs decrease in the first six months but recover thereafter up to two yr after kidney transplantation. Such a decrease is favored by high levels of tacrolimus but not by induction protocols with anti-CD25.

Kinetics and cellular site of glycolipid loading control the outcome of natural killer T cell activation

CD1d-restricted natural killer T cells (NKT cells) possess a wide range of effector and regulatory activities that are related to their ability to secrete both T helper 1 (Th1) cell- and Th2 cell-type cytokines. We analyzed presentation of NKT cell activating α galactosylceramide (αGalCer) analogs that give predominantly Th2 cell-type cytokine responses to determine how ligand structure controls the outcome of NKT cell activation. Using a monoclonal antibody specific for αGalCer-CD1d complexes to visualize and quantitate glycolipid presentation, we found that Th2 cell-type cytokine-biasing ligands were characterized by rapid and direct loading of cell-surface CD1d proteins. Complexes formed by association of these Th2 cell-type cytokine-biasing αGalCer analogs with CD1d showed a distinctive exclusion from ganglioside-enriched, detergent-resistant plasma membrane microdomains of antigen-presenting cells. These findings help to explain how subtle alterations in glycolipid ligand structure can control the balance of proinflammatory and anti-inflammatory activities of NKT cells.

Role of NK and NKT cells in solid organ transplantation

In the context of solid organ transplantation, the exact interactions between the innate and adaptive alloimmune response have not yet been fully explored. In this transplant setting, natural killer (NK) cells have emerged as a particular focus of interest because of their ability to distinguish allogeneic major histocompatibility complex (MHC) antigens and their potent cytolytic activity. Based on this observation and its potential clinical relevance, NK cells have recently been shown to participate in the immune response in both acute and chronic rejection of solid organ allografts. Numerous experimental and clinical studies demonstrate that NK cells determine transplant survival by rejecting an allograft not directly but indirectly by providing bystander effects. In addition, NK cells are influenced by immunosuppressive therapies such as calcineurin inhibitors or steroids. As NK and natural killer T (NKT) cells have also been shown to play a profound role in allograft tolerance induction, this review summarizes the major findings to highlight the functional role of these lymphocyte subsets, which may constitute an underestimated mechanism affecting graft outcome in solid organ transplantation.

Prolongation of cardiac allograft survival by rapamycin and the invariant natural killer T cell glycolipid agonist OCH

BACKGROUND

Invariant natural killer T (iNKT) cells are glycolipid-responsive cells with potent immunomodulatory properties. Although iNKT cells have been implicated in cardiac allograft tolerance, whether in vivo triggering of iNKT cells with Th2-promoting glycolipids offers a therapeutic benefit in heart transplantation remains unexplored.

METHODS

C3H (H-2k) hearts were transplanted into C57BL/6 (H-2b) mice. The recipients were left untreated or received the Th2-promoting iNKT cell agonist OCH, the antirejection agent rapamycin, or both. Allografts were recovered on postoperative day 8 or at endpoint, stained with hematoxylin-eosin, and analyzed for intragraft transcript levels of effector cytokines and iNKT cells' invariant T-cell receptor segment Valpha14-Jalpha18. The presence of circulating alloantibodies was assessed in recipients' sera at similar time points. A second fully mismatched cardiac allograft model (BALB/c-to-C57BL/6) was used to further validate the efficacy of our treatment regimens.

RESULTS

Combination immunotherapy with OCH and rapamycin significantly enhanced C3H allograft survival and led to nearly normal graft histology with minimal vascular changes and mononuclear cell infiltration, and an almost normal IgG1:IgG2a ratio in recipients' sera. These were accompanied by elevated intragraft mRNA levels of interleukin (IL)-4, and to a lesser extent IL-10 and IL-13, and high transcript levels of Valpha14-Jalpha18 T-cell receptor gene segment. Furthermore, when used alone or together with rapamycin, OCH delayed allograft rejection in our BALB/c-to-C57BL/6 model.

CONCLUSIONS

In vivo administration of OCH may deviate alloimmune responses towards a Th2 phenotype and prolong allograft survival. Select iNKT cell glycolipid agonists can therefore be used in monotherapy or combination immunotherapy of transplant rejection.

Bronchoalveolar immunologic profile of acute human lung transplant allograft rejection

Bronchoalveolar lavage fluid (BALF) offers a potential means to diagnose acute rejection and could provide insight into the immune mechanisms responsible for lung allograft rejection. Transbronchial biopsies from 29 bronchoscopic procedures were assessed for rejection. Concurrent BALF lymphocyte subsets were examined by flow cytometry, including CD4 and CD8 T cells and their activation status by CD38 expression, natural killer (NK), NK-like T (NT), B, regulatory T, and invariant receptor NK-T cells. Percentages of CD4 were reduced, and CD8 and activation of CD4 T cells correlated with rejection. There were trends for increased NT, reduced NK, and increased B cell percentages with rejection, suggesting potential roles of these cells. Among regulatory cells, the percentages of regulatory T cells decreased and CD4/CD8 invariant NK-T cells increased during rejection, suggesting a proinflammatory profile. A unique BALF lymphocyte profile was associated with rejection and may provide insight into the pathogenesis of allograft rejection.

Natural killer T cells: a bridge to tolerance or a pathway to rejection?

Over the past 20 years, natural killer T (NKT) cells have been shown to play an important role in both innate and adaptive immune responses. In this review, the potential role of NKT cells in transplantation will be discussed, particularly their role in rejection and the induction of a state of tolerance.